Perithecia have been collected only on Aristotelia sp. and only in Canterbury. In the North Island, as with other species of powdery mildew, only the oidium conidial form is present. It was first recorded from New Zealand by Berkeley (1855) on the indigenous host Aristotelia as Erysiphe densa. Salmon (1900) showed this fungus to be a synonym of E. polygoni. In the autumn it is very common throughout the country, but only when weather conditions are unfavourable are losses in fodder crops such as swede and rape likely to become severe. Brien, Chamberlain et al. (1955) reported that it may cause dwarfing and distortion of pea plants. Except for the two species of Aristotelia and Geum urbanum all host plants are introduced cultivars.